For the time being you can use the following workaround:
		<telerik:RadEditor ID="RadEditor1" runat="server" ></telerik:RadEditor>
		<script>
			var oldExecute = Telerik.Web.UI.Editor.InsertLinkCommand.prototype.onExecute;

			Telerik.Web.UI.Editor.InsertLinkCommand.prototype.onExecute = function () {
				this.linkProperties.href = encodeURI(this.linkProperties.href);
				oldExecute.call(this);
			}
		</script>